feat(branding): install @vite-pwa/assets-generator + config

Adds pwa-assets.config.ts that reads $BRAND_DIR (default
./branding/default) and $BRAND_APP (optional per-standalone
override), resolves logo.svg/logo.png with documented fallback
order, and emits the existing icon set (favicon.ico,
icon-{192,512}.png, icon-maskable-{192,512}.png,
apple-touch-icon.png) into public/icons/.

Generator outputs alongside its source, so the config stages the
brand source into public/icons/.brand-source.{svg,png}; gitignoring
public/icons/ covers both staged source and generated icons in one
line.

Adds pnpm script `generate-pwa-assets`. Vite configs / HTML <link>
href updates come in follow-up commits; this commit alone produces
the icon set under public/icons/ but doesn't yet replace the
committed public/*.png binaries.

Part of aiolabs/webapp#95 (brand kit architecture).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pwa-assets.config.ts

@@ -0,0 +1,54 @@
+import { defineConfig } from '@vite-pwa/assets-generator/config'
+import { copyFileSync, existsSync, mkdirSync } from 'node:fs'
+import { join, resolve } from 'node:path'
+
+const BRAND_DIR = process.env.BRAND_DIR ?? './branding/default'
+const BRAND_APP = process.env.BRAND_APP ?? ''
+
+const candidates: string[] = []
+if (BRAND_APP) {
+  candidates.push(
+    join(BRAND_DIR, 'icons', BRAND_APP, 'logo.svg'),
+    join(BRAND_DIR, 'icons', BRAND_APP, 'logo.png'),
+  )
+}
+candidates.push(
+  join(BRAND_DIR, 'logo.svg'),
+  join(BRAND_DIR, 'logo.png'),
+)
+
+const source = candidates.find((p) => existsSync(p))
+if (!source) {
+  throw new Error(
+    `No brand logo found. Tried:\n  ${candidates.join('\n  ')}\n` +
+      `See branding/README.md for the brand kit contract.`,
+  )
+}
+
+// The CLI emits next to the source. Stage into public/icons/ so generated
+// PNGs are served at /icons/<name>.png and a single .gitignore line covers
+// the whole tree.
+const stagingDir = resolve('public/icons')
+mkdirSync(stagingDir, { recursive: true })
+const sourceExt = source.toLowerCase().endsWith('.svg') ? '.svg' : '.png'
+const stagedSource = join(stagingDir, `.brand-source${sourceExt}`)
+copyFileSync(source, stagedSource)
+
+export default defineConfig({
+  headLinkOptions: { preset: '2023' },
+  preset: {
+    transparent: {
+      sizes: [192, 512],
+      favicons: [[48, 'favicon.ico']],
+    },
+    maskable: { sizes: [192, 512] },
+    apple: { sizes: [180] },
+    assetName: (type, size) => {
+      if (type === 'transparent') return `icon-${size.width}.png`
+      if (type === 'maskable') return `icon-maskable-${size.width}.png`
+      if (type === 'apple') return 'apple-touch-icon.png'
+      throw new Error(`Unknown asset type: ${type}`)
+    },
+  },
+  images: [stagedSource],
+})